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Chemistry · Glossary

What is Dehydration of an alcohol?

Also known as: dehydration

Definition 22.10 University Chemistry — Year 1 · Chapter 22 — Alcohols: Activating the OH Group

The dehydration of an alcohol is the elimination of water, catalysed by a strong acid (sulfuric or phosphoric acid) and heat, giving an alkene: R2CH−CR2′OH→R2C=CR2′+HX2O\mathrm{R_2CH{-}CR'_2OH} \to \mathrm{R_2C{=}CR'_2} + \ce{H2O}.

Acid-catalysed dehydration of 2-methylbutan-2-ol (E1): protonation, loss of water to the tertiary carbocation, loss of a proton. Removing the proton from the CH2 gives the trisubstituted 2-methylbut-2-ene (Zaitsev, major); from a methyl group, 2-methylbut-1-ene (minor). Acid-catalysed dehydration of 2-methylbutan-2-ol (E1): protonation, loss of water to the tertiary carbocation, loss of a proton. Removing the proton from the CH2 gives the trisubstituted 2-methylbut-2-ene (Zaitsev, major); from a methyl group, 2-methylbut-1-ene (minor).
Acid-catalysed dehydration of 2-methylbutan-2-ol (E1): protonation, loss of water to the tertiary carbocation, loss of a proton. Removing the proton from the CHX2\ce{CH2} gives the trisubstituted 2-methylbut-2-ene (Zaitsev, major); from a methyl group, 2-methylbut-1-ene (minor).
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